The invention relates to a circuit arrangement for operating a lamp, comprising
supply input terminals for connection to a supply voltage source,
a rectifier coupled to the supply input terminals for rectifying an AC supply voltage supplied by the supply voltage source,
an inverter equipped with input terminals coupled to respective output terminals of the rectifier for generating a high frequency lamp current out of a DC voltage,
a first unidirectional element D1 coupled between a first output terminal of the rectifier and an input terminal of the inverter,
a first branch that is coupled between a terminal N1 between the first output terminal of the rectifier and the first unidirectional element and a terminal N2 in the inverter on which during operation of the circuit arrangement a high frequency voltage is present.
The invention also relates to a compact lamp equipped with such a circuit arrangement.
A circuit arrangement as mentioned in the opening paragraph is known. The known circuit arrangement incorporates power feedback realized by the first unidirectional element and the first branch. Because of this power feedback the power factor of the known circuit arrangement is relatively high although the topology of the known circuit is relatively simple and therefore relatively cheap. Disadvantages of the known circuit arrangement are a relatively low efficacy and the fact that it is very difficult to restrain the EMI.
The invention aims to provide a circuit arrangement for operating a lamp that is relatively cheap and simple, has a good power factor combined with a relatively high efficacy and offers a good EMI restrain.
A circuit arrangement as mentioned in the opening paragraph is therefore according to the invention characterized in that the circuit arrangement is further provided with
a second branch comprising a series arrangement of a second (D2), a third (D3), a fourth (D4) and a fifth unidirectional element (D5) that connects the input terminals of the inverter,
a third branch comprising a first capacitive element C1 and connecting a cathode of the second unidirectional element with an anode of the fourth unidirectional element,
a fourth branch comprising a second capacitive element C2 connecting an anode of the fifth unidirectional element with a cathode of the third unidirectional element,
a fifth branch connecting a terminal N5 between the third and the fourth unidirectional element with the terminal N2.
It was found that a circuit arrangement according to the invention has a good power factor. In addition it was found that the efficacy of a circuit arrangement according to the invention is relatively high and that the EMI could easily be restrained.
It is advantageous to equip a circuit arrangement according to the invention with a sixth branch comprising a third capacitive element (C3) and coupling a cathode of the first unidirectional element to terminal N5. This third capacitive element controls the amplitude of the voltage present at the terminal N5 and can be so dimensioned that a further improvement in the shape of the current supplied by the supply voltage source is realized.
Good results were obtained for a circuit arrangement according to the invention, in which the inverter comprises a bridge circuit that is equipped with a seventh branch comprising a series arrangement of two switching elements and in which the terminal N2 is a terminal of the seventh branch between the two switching elements.
Good results have also been obtained for embodiments of a circuit arrangement according to the invention, in which the first branch comprises capacitive means.
Since a circuit arrangement according to the invention has a relatively simple topology, it can be manufactured so that it is very small. For this reason a circuit arrangement according to the invention is very suitable to be used in the ballast means of a compact lamp comprising
a light source provided with a vessel that is closed in a gastight manner and transmissive for visible radiation,
a housing connected to the light source and provided with a lamp cap,
ballast means electrically connected to the light source for operating the light source and positioned at least partly in a space surrounded by the housing.